Range is one of the attributes in the Respawnables, and it defines how far a gun can shoot while still being able to deal damage. This is shown by the "Range" attribute of a weapon. The more bars present, the longer the range. However, it does not represent the most effective distance is for a weapon.
All Sniper Rifles have a range of 4 bars while some Shotguns have 1, and most launcher type weapons have 2-4 bars. Generally, automatic shot weapons have a longer range (3-4 bars) than single shots (1-2 bars). Note that this is a rule of thumb, and is not always accurate.
For example, the Automatic Shotgun has poor range despite being an automatic weapon (as it is considered as a shotgun), and the Thumper has great range despite being single shot weapon (it is considered as a launcher typed weapon).
Explosive weapons though (apart from grenade-launching weapons) do not follow this rule, as they usually have unlimited range and are able to hit anywhere on the map.